


Under a Day

by JupiterIsaJellyfish



Series: Cryptid Found Footage: The Leviathan [11]
Category: Leviathan - rest_in_rip, 僕のヒーローアカデミア | Boku no Hero Academia | My Hero Academia
Genre: Leviathan!Izuku, Midoriya Izuku Has a Quirk, Parental Aizawa Shouta | Eraserhead, Shinsou is a good friend, This Is Fine, forced transformation
Language: English
Status: Completed
Published: 2018-10-19
Updated: 2018-10-22
Packaged: 2019-08-04 14:27:14
Rating: Not Rated
Warnings: No Archive Warnings Apply
Chapters: 2
Words: 4,077
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/16348436
Author URL: https://archiveofourown.org/users/JupiterIsaJellyfish/pseuds/JupiterIsaJellyfish
Summary: Midoriya and Shinsou have a run in with an upset student, and it makes everyone's day a lot harder





	1. Just a Day

**Author's Note:**

  * Inspired by [Leviathan](https://archiveofourown.org/works/13216827) by [rest_in_rip](https://archiveofourown.org/users/rest_in_rip/pseuds/rest_in_rip). 



> This message is brought to you by the letter L, go read Leviathan if you haven't already okay cool 
> 
> Tbh I don't have an excuse for why this took so long, it's actually been written for a while now. Anyway, thanks to nameless_void for the prompt, finger-guns to you

Hitoshi had actually been having a pretty good day up until they got off the train. He’d had a petty argument with his foster-mom and wanted to decompress away from the house. When Midoriya heard about it he’d immediately invited Hitoshi to spend the afternoon at his place. It was Saturday so they got out after lunch, the weather was cooling down, and he was with his friend. 

All things considered, a pretty good day. 

Not for everyone though, apparently. 

He barely noticed her on the train. He and Midoriya had been talking about nothing, homework and memes and whatever, when he’d glanced up and noticed the red cat-ear headphones on the only other head in the train car. What really stood out to him though was that she was crying. 

He kept listening to Midoriya’s scattered rambling in one ear while occasionally letting his periphery drift back to her. She was hunched over a cellphone, shoulders shaking, face hidden by curly plum hair. She must have been a middle schooler; he recognized her uniform from a brief stint at the same school two years ago. 

He cringed inside when he heard her let out another staccato sob. 

A battered corner of his soul wanted to go over and ask her what was wrong, but he was a stranger with a -2 proficiency in social situations. It was none of his business. The smarter part of him tuned back in to what Midoriya was saying. He didn’t notice her again until they reached their stop. 

She left the car just before they did, still shuddering as she adjusted her cat headphones and slowly shuffled ahead of them. Hitoshi thought he could make out the thrum of the base even from a meter behind her. That couldn’t be healthy. 

He shrugged it off and tried to focus back on Midoriya.

Midoriya still hadn’t noticed her- if he had he probably would be shooting them both conflicted glances. Instead he was staring at the pavement, walking in silence. Something dark flashed in his eyes, and Hitoshi started to wish he’d actually been paying attention to what he’d been saying.

He really started to wish he’d been paying attention when Midoriya suddenly sped up and slammed straight into the girl. 

A lot happened very quickly. 

Midoriya backpedaled a half step, fins flaring as he deftly raised a hand to defend from the yet unseen threat. The girl whirled around, shoulders climbing up to her ears, fists clenched and teeth bared. Hitoshi’s sleep addled brain had trouble keeping up as she shrieked “WH _at w_ AS _That_ fOr?” 

Hitoshi raised his eyebrows at her voltage of hostility, taking in her tear streaked face and bloodshot eyes. Midoriya saw it too, his fins folding back and hands lowering in placation, “I’m- I’m so sorry I-”. 

But it was too late; he’d broken the dam. Mouth still twisted in a snarl, the girl curled in on herself and started to wail, headphones slipping down her head dangerously. Midoriya cautiously stepped forward, reaching out either to catch the headphones or offer comfort. Either way it must have been the wrong move, because the girl caught sight of the motion and reeled back. 

_“Don’t touch me!_ ” she snapped, slapping him away with her hand. With her glowing hand. Had it been glowing this whole time or-?

He didn’t have time to mull it over because almost immediately Midoriya staggered back, clutching the side of his head and- oh no. 

Okay Hitoshi’s awake now. 

Midoriya spasmed in an oh-so-familiar way, collapsing to his knees as scales shot across his face and arms. Hitoshi only had seconds to act before-

“Midoriya!” he barked, praying Midoriya would recognize the lifeline. He must have, because he opened his mouth to respond, but the only thing that came out was a pitched rumble. That wasn’t enough, Hitoshi’s quirk needed a more focused response, and so all he could do was watch in fascinated horror as Midoriya fought back the Leviathan. 

He’d almost forgotten about the girl, who’d abruptly gone silent. Out of the corner of his eye he saw her fall backwards, and the wretched fear frozen on her face. After a split second he decided to trust Midoriya enough to look away, pivoting to face her. 

“What did you do?” he demanded. She lifted a shaking gaze and stammered, “I don’t- I didn’t mean-!” and her face went slack. 

Okay, good, one less variable. 

Now back to the tormented lizard friend. 

Midoriya wasn’t so good. Spikey teal fins ran parallel down his spine to his frilled tail, dark scales coated his body, and he had a mouth full of teeth. He wasn’t spasming anymore though. Instead he stayed almost completely still, and somehow that felt even worse. Hitoshi started to kneel down, determined to try and reassure him, when one of Midoriya’s splitting eyes darted to meet his. 

And then in a blink he was gone. 

Hitoshi barely caught sight of the flash of black and green shooting down the alleyway just ahead of him. Tension bled out of the air, and Hitoshi looked around only to suddenly realize how precarious that had been. 

This was a normal city street, with windows and apartment doors all very capable of housing an unsuspecting pair of eyes. The fact that there was only one pair of eyes to deal with was something of a miracle.

Hitoshi took a deep breath and glanced over at the passive middle schooler sitting on the sidewalk, the dull boom of a base beat still emanating faintly from the headphones. He shuffled over to kneel in front of her and cleared his throat. 

“Tell me what your quirk does,” he ordered. He was still working out how to interrogate with Brainwash, but he’d had some practice. 

The girl straightened to look him in the eye before answering robotically, “My quirk is Catalyst. It is the ability to forcibly activate quirks by touching someone”. 

Oh that’s… great. It explained a lot, anyway. But the city wasn’t a sparking pile of dust yet, and his bones weren’t iced over with the knowledge of his own mortality, so maybe Midoriya could still control Leviathan now even with it activated. 

“Tell me how we stop its effects,” he said. 

“We cannot stop it after I touch someone. Its effects last longer depending on my emotions. If I feel very emotional, it can last for a day,” she responded. 

Crap. If ‘very emotional’ earned a day, then Midoriya was in for a rough time. Somewhere in the back of his head Hitoshi was increasingly curious to know why she’d been so upset, but he knew better than to pry. It still wasn’t his business. What was his business was figuring out how to keep Midoriya a secret. He couldn’t let her remember what she’d seen, not without risking his safety. 

“You are going to continue to where you were going, and you’re going to forget the last five minutes,” he instructed.  
Here’s to hoping this worked. 

She got up, headphones askew around her neck, and started walking away down the street. As she did, a businessman with a briefcase and a small family of tourists emerged from the station and strolled past him, casually sidestepping him and Midoriya’s discarded yellow backpack. 

Shoot, He really needed to find Midoriya. 

Picking himself up and hefting the second backpack (damn, how did Midoriya carry this thing everyday?) he tried not to look suspicious as he stepped into the shadow of the alleyway. 

He wasn’t quite sure what he was looking for, Midoriya or the Leviathan or something in between, and come to think of it he wasn’t even sure if Midoriya was down here with how fast he could be. Still, he had to try. 

About halfway down the alleyway he was hit with sudden inspiration and whisper-shouted “Midoriya?”

Almost immediately there was a suspicious scraping of plastic and brick and scales, and something inky glittered just ahead of him. Sure enough, as he slowly crept closer he could make out scales and fins determinedly hidden underneath an empty dumpster. 

“Hey, you hearing me alright?” He murmured. 

The stripes and fins shifted sluggishly, until slowly, dark claws extracted a glimmering serpentine body. 

He was only a few meters long, and utterly miserable. He stayed low to the ground, pressed between the trash and the wall, and half-heartedly flickered a few Chernobyl-disaster eyes in Hitoshi’s direction. 

Despite his friend’s obvious unhappiness, Hitoshi was flooded with relief. Midoriya was still in control. His parlay with the Leviathan held, even though it looked like neither of them were enjoying it. 

Hitoshi put down the backpacks to sit a few feet from his friend.

“I talked to that girl- hey no wait,” he interrupted himself when Midoriya flinched, “I ordered her to forget what she saw, it should be alright- I interrogated her, and she said her quirk forces people’s quirks to activate. She um, she can’t control when it wears off, and it lasts longer when she’s upset”. 

Midoriya’s many eyes narrowed and tiny green lights flashed as he shifted in agitation. Hitoshi grimaced in agreement, not sure what he could say to be comforting. Now that everything was said and done and he let himself reflect, it was glaringly obvious how much he could have done to prevent this. It would have been so easy, if he’d just-

A pocket-sized peal of thunder resounded from Midoriya. Hitoshi looked up and saw Midoriya staring right at him, looking miffed. “What-?”

Midoriya snorted a puff of charged air in Hitoshi’s face, making his hair fizzy with static. Hitoshi blinked rapidly. It took him a second, but the mildly unimpressed look on Midoriya’s face gave him the gist of the message: _I can smell you beating yourself up and it needs to stop_.

Hitoshi swatted a harmless hand at Midoriya’s snout. Okay, fine, business then. 

He stared at the wall for a moment to think about their most immediate problems. 

“Okay, so if this isn’t going to wear off for a while, you probably don’t want to go home right now do you?” he asked. Midoriya shook his head slightly, only to pause and look thoughtful. 

With a swan-like arch of his neck he gestured at his backpack. Hitoshi raised an eyebrow before leaning back and dragging it closer. 

Midoriya jabbed the side pocket, which Hitoshi opened to discover Midoriya’s phone. 

Oh.

“Do you want me to text your mom for you?” 

Midoriya nodded. 

“Does she… know?” 

Midoriya hesitated, then nodded again, a bit unsteadily. 

Hitoshi was no expert on longstanding familial relationships, but he figured telling your mom that you were stuck as a convicted hellbeast might not be too fun. He frowned thoughtfully, then wondered “could I just tell her you decided to stay with me for the night instead?”

It was actually kind of amazing how expressive Midoriya was despite being a eldritch sea monster. His fins folded back in dislike, but he nodded again. It was a good idea and also he hated it. 

Hitoshi followed Midoriya’s directions for the passcode and sent the text. He then stuffed the phone in his pocket for now and stared at the ground. 

Now what. 

Suddenly Midoriya shifted, rising to his feet and turning away. He didn’t quite meet Hitoshi’s eyes as he slunk around the dumpster and looked up at the towering walls above them. Hitoshi waited for him to look back, but he didn’t. The message was pretty clear: _I’m going now_. 

Hitoshi’s frown deepened as he heaved himself off the concrete, but he wasn’t going to argue. He wasn’t expecting Midoriya to stay hidden in a dumpster for however long this lasted. For all he knew Midoriya was just barely keeping the Leviathan complacent, and this was no place to spend a hard night.

“I’ll keep your stuff safe, and I’ll cover for you if your mom texts back. I think I’m going ask Aizawa if I can spend the evening at his apartment, so if it wears off early I’ll probably be over there”. 

Midoriya nodded one last time, and then in a dark blur he was gone again. 

Hitoshi stood still and took a steadying breath, then fished out his phone and opened his messaging app.

_‘Sensei, would it be alright if I went to your apartment? Something happened to Midoriya that you’ll probably want to know about’_.

He hadn’t even reached the street when his phone started ringing. 

He checked the contact- Aizawa- and accepted. 

“Shinsou, I need you to tell me everything”.


	2. For a Day

**Summary for the Chapter:**

> Izuku is stuck as the Leviathan for a day

**Notes for the Chapter:**

> I would have posted this yesterday but I ended up chilling with my folks instead.

Of all the emotions Izuku had ever expected to feel from the Leviathan, _indignation_ was not one of them.

When the Leviathan started rumbling contentiously on the train, he’d just smothered it on reflex. He was way too used to it refusing to shut up to think about it, especially when it kept screaming at him while they got off the train. 

In his mounting frustration, he’d slammed right into that girl. 

And apparently right into the problem. 

It was a shock when, as he was crippled by the burning sensation of fins shooting down his spine, he realized the Leviathan wanted nothing to do with this. All it was forcing on him was the intensity of its scorn… 

Thank Neptune for Shinsou. 

So here he was, curled up on top of a building, trying to plan his next move. 

Everything about this situation felt surreal. He was stuck in the Leviathan’s form (weird), but it wasn’t trying to take control (very weird), and nothing had gone horribly wrong yet (mind blowing). 

The ambiance of Leviathan’s furious hissing bubbled in his mind as he peered over the roof ledge. It didn’t help his calm but honestly he could relate. From what Shinsou has said this could last a day, which meant he’d have to spend the next 24 hours trying not to be-

The Leviathan’s grumbling erupted into a screech and it janked their neck eastward, over towards the glimmering horizon and… 

Oh. 

_Duh._

The hissing lowered back to a simmer as Izuku slowly unraveled and plotted a course. He wasn’t used to helming this form- in the past he’d either been too busy choking the Leviathan or being fundamentally dead inside. If he thought too much about moving he started to get nauseous. So, no thinking, only action, because thinking meant analyzing how seven-limbed parkour worked. 

In a blink, he’d leapt across the next block. 

Soon the world became an opaque blur around him as he traversed the multi-surfaced roofs of Musutafu. He tried to stick to the uninhabited shadows, ignoring the bustle of the afternoon rush below him. Every now and then he would be cuffed with the sense that there was a person hanging laundry or making a call ahead, and he’d have to diverge down into an alley or around a line of chimneys. As long as there weren’t any earsplitting shouts, he knew he was okay. 

And then he saw it. 

Bit’s abandoned building, sitting just between him and the sea. 

It rose several stories above the ten level apartment building he’d just scaled and stood on the other side of a reasonably busy street. Izuku barely noticed, taking a flying leap and literally soaring across the gap and onto the side-facing fire escape, landing with a restrained **thud**. He didn’t lose momentum, instead rebounding off the metal and rushing up the building’s austere walls, fast as a shadow.

The roof was blissfully vacant, and Izuku heaved in a deep breath. 

Okay, he’s safe up here. 

The rough weathered stone was sunbaked despite the cool afternoon air and the smell of the ocean clipped the breeze. The lip of the roof easily concealed him from the bustle of the lunch rush, leaving him free to stand still and enjoy a moment of calm. 

The sheer familiarity of the place settled him, and he started to have second thoughts about heading straight for the safe, cold embrace of the deep. 

He and Bit had spent countless hours up here, goofing off and trying not to get impaled by shrapnel. Somehow though he’d never been up here in broad daylight, when the warmth reflecting off of the cement combined with the soothing hum of city life.

He wasn’t in any danger of being caught up here (by anyone who would be taken seriously) and he had a lot of time to kill. 

Izuku slunk around one of the decommissioned ventilation boxes and lay down in the direct sunlight. Something peaceful seeped through him in the wake of the past half hour’s adrenaline. 

Why not enjoy the atmosphere, and the sun… 

\-----

The sound of labored breathing and footsteps woke him up approximately 1.975 seconds before the sound of the scream. His head jerked up while he was still half asleep and he saw a messy graphic T-shirt and worn out jeans before the door of the stairwell slammed shut. 

There was a moment, just before his mind caught up, when he heard himself think ‘ _is it possible for reptiles to get heart attacks?_ ’

And then his mind did catch up, and he immediately hurled himself bodily towards the ocean with all the panicked grace of a dying albatross. 

He didn’t question how he made the distance, breaking the surface just a couple of meters past the shoreline, then diving at the speed of fast. 

It wasn’t until he was a ways out that he dared to slowly come to a stop on the barren sand. An endless gradient of blue stretched ahead of him, the purple of dying sunlight bleeding through the water. It should have been a relief. 

It was not. 

There were a few times in Izuku’s life when his internal screaming outmatched the Leviathan’s. This could’ve been one of them.

Crap, someone had _seen_ him. 

Izuku shook his head unsteadily, letting the weight of the water cushion the movement. 

No, he’s okay. Who ever it was probably hadn’t gotten a good look at him, and they didn’t have any proof that it was _him, its okay, he’s okay._

The persistent shove of the current cottoned to his sides, and he breathed deeply. 

_He’s fine._

The paranoid part of him wasn’t convinced. But what was he supposed to do? Go up and check to see if they were still up there, like some forlorn cartoon mermaid? Nope, that was a one-way ticket to getting caught. Again. 

No, better to just keep going, down where nobody would find him. Down where he’d be safe.

\-----

He spent the next nameless hours weaving across the sandy plains, watching rocks and somber fish float past him, dimly aware of the unremarkable downfall of the sun.

Swimming was impossibly effortless. A part of him knew exactly where he was and exactly how far he was from where he’d started, and the rest of him didn’t care. 

By the time he crossed over the shelf his eyesight had faded to a muted green. 

There, hanging in the abyss, he had a thought. He deliberately stretched his reflexive grip on the Leviathan, and let its begrudging contentment consume them. It was deliberate enough that it was almost painless, and in a heartbeat he outweighed his apartment.

Almost insignificant, and completely safe. 

Every now and again he’d sense something. A ship passing by somewhere overhead, something large swimming below him, or a crumbling boom echoing out of the earth. None of it bothered him. There was nothing out here to hurt him, and what out here would dare even try. 

The sun slowly dragged itself back up into the sky and Izuku barely cared. Over time he’d sunk down almost a kilometer, to where the infant rays of light only just registered even to his adapted eyes. After hours of effortless swimming, he felt content to float aimlessly for a while, coated in the faint touch of daylight. 

It was then, after some uncounted span of time, that something broke. 

That, and Leviathan’s roar of (assumedly) surprise, was enough to snap him back to complete consciousness. For a second all he knew was that he was getting smaller, and then it clicked. His time was up. 

A mental jerk was enough to put Izuku back in control, before he purposefully arced himself back upwards. He wasn’t quite sure what time it was, or how long he’d been out here, but he did know how far he was from land. He regained some of the Leviathan’s size for speed and shot back towards the shore. When he reached the sandbeds he forced himself to shrink back down, letting himself ignore the Leviathan’s snarls of disappointment. 

He avoided the areas he knew would be swarming with Sunday swimmers and made a beeline for Dagobah Beach. It was distinctly less treacherous after months of being scavenged by he and Bit, but the few unmovable skeletons of rust and countless buried metal fragments still kept most people away. 

He cautiously raised his eyes out of the water to scan for bystanders. 

No movement caught his eye, which was good. One thing did stick out to him though, its colors fading but still distinct. 

His yellow backpack, sitting neatly on the shell of busted car, next to a black sports bag.

Izuku hauled himself out of the water and approached it warily. Sure enough, it was his backpack, which Shinsou had apparently taken with him to Aizawa’s apartment. A note was pinned to the front, written in the same handwriting that had given him a B- on his last heroics essay. 

** Midoriya -  **

** Shinsou told me what happened. I dropped these by after my shift.  
I want you to call me as soon as you can.  **

** \- Aizawa **

Izuku read the note a few times, processing its simplicity. Okay, great, a phone call. To his pro-hero teacher. But he’s probably not in trouble. _Deep breaths Izuku_. Wait how did Aizawa know he’d be at Dagobah Beach? 

He gingerly snagged both the backpack and the black bag with his teeth, and dragged them over to a shipping container soaked through with rust. Inside the black bag were clean clothes, including orange basketball shorts and a black T-shirt with an eyepatched hello kitty icon. The first words out of his mouth were a muttered thanks for Aizawa’s existence. Dry clothes had never felt better. It only took a little bit of digging in his backpack to find his phone, and he immediately pulled up the messaging app.

`Me:  
Hey Mom, is it okay if I spend the night at Shinsou’s instead?`

`Mom:  
I suppose? You’ll still come by to get your things though right?`

`Me:  
His foster parents have everything I’ll need so no`

Izuku cringed a bit at Shinsou’s lack of tact, but kept reading.

`Mom:  
Okay, but tell me the address`

`Me:  
208 East Saleucami St.`

`Mom:  
Alright. Call me in the morning Izu!`

`Me:  
Ok.`

Izuku mentally added his mother to his call list, then set his phone aside to slide on the flip-flops Aizawa had packed him. He then folded the sports bag and stuffed it into his backpack, picked himself up, and dialed Aizawa’s number. 

It picked up immediately. 

“Midoriya, are you alright?”

“Hi, Sensei. Yeah, I’m okay, just tired”.

“Hm. I want you to see me after class tomorrow to give me relevant details. You know how dangerous that could have been, right? For you and everyone involved”.

Izuku cringed, “yeah, you don’t have to tell me. I think it’s okay, but there were some close calls”.

Aizawa made a vague affirming noise, like he was pinching the bridge of his nose. He probably was, actually. 

“Let me know if that impression changes. I haven’t heard reports of anything resembling the Leviathan from the police, but it’s too soon to know. Stay low for now, and get some rest”.

“Yes sir. Also, sensei, how did you know where I’d be?”

“I keep track of all of my problem students,” Aizawa replied dismissively, and Izuku suspected that was all the answer he’d get, “now rest”.

“Yes sir,” and then Aizawa hung up. 

Izuku sighed before tapping back to his mother’s contact. It went to voicemail, so he left her a quick message that he was heading home. A glance at the time told him it was 10. 

It’d been just under a day. 

Izuku hefted his backpack, set his shoulders, and walked out into the sunlight.

**Notes for the Chapter:**

> Who saw him on the roof? Does it even matter? Will I ever quit it with the hypotheticals? The world may never know. 
> 
> A lot of commenters were asking about seeing Leviathan in the ocean so I hope this manages to check that box for most people.  
> Also chances are I won't be able to update much in the coming weeks but who knows

**Author's Note:**

> (warning, very very sad) Sidenote- the girl was crying because her mom was found dead; AfO killed her for her quirk, since catalyst is pretty similar to the one he used in the kamino fight ¯\\_(ツ)_/¯
> 
> Are Japanese trains ever that empty? Are Japanese city streets ever that empty? The answer is no but I can dream


End file.
